动态拼接LINQ 查询条件

本文章转载：http://www.cnblogs.com/wangiqngpei557/archive/2013/02/05/2893096.html

参考：http://dotnet.9sssd.com/entfwk/art/960

 http://www.cnblogs.com/killuakun/archive/2008/08/03/1259389.html

http://www.cnblogs.com/snowdream/archive/2008/07/18/1246308.html

以往我们都是通过判断的方式来拼接查询的SQL字符串，但是现在我们面对是强类型的LINQ查询，是否可以很方便的进行类似查询。

eg:

string _UserID = string.Empty;

           _UserID = "E351D301-F64B-412C-B9EF-573F41235AF2";

 

           string _UserName = string.Empty;

           _UserName = "admin";

 

           string _employyName = string.Empty;

           _employyName = "测试1";

 

           using (var xj = new XJGasBottles_testDataContext())

           {

               //Linq写法

               var usersLinq = from us in xj.Users

                               where (string.IsNullOrEmpty(_UserID) || us.UserID.ToString() == _UserID)

                                      && (string.IsNullOrEmpty(_UserName) || us.UserName == _UserName)

                                      || (us.EmpName == _employyName)

                               //where string.IsNullOrEmpty(_UserID) || us.UserID.ToString()==_UserID

                               //where string.IsNullOrEmpty(_UserName) || us.UserName==_UserName

                               select us;

               foreach (var item in usersLinq)

               {

                   Console.WriteLine("Linq:");

                   Console.WriteLine(item.UserID + "_" + item.UserName);

 

               }

 

               //Lamda写法

               var usersLamda = xj.Users.Where(s => (string.IsNullOrEmpty(_UserID) || s.UserID.ToString() == _UserID) &&

                                               (string.IsNullOrEmpty(_UserName) || s.UserName == _UserName) ||

                                               (s.EmpName==_employyName)

                                         )

                                   .Select(s => s);

 

               foreach (var item in usersLamda)

               {

                   Console.WriteLine("Lamda:");

                   Console.WriteLine(item.UserID + "_" + item.UserName);

 

               }

 

           }